How use spaces instead of underscores in file names?
This bug was fixed (at 2015-10-15), so the easiest solution is to download nightly build of Blender: https://builder.blender.org/download/ . I have tried it and now I finally can save my files as usually. The fix also will be available in 2.76a and later releases. Alternatively, you can build Blender yourself. The bug was fixed by this patch: https://developer.blender.org/rB767d3f23b7efb4e993574c29ebbbe0a4d90f5e50 .